胃の内容物から見たブリの食性-I

Abstract

This report is of some feeding habits, one of the several results brought about by the author in his yellow-tail investigations. The stomach contents of the 107 yellow-tails, which were caught mainly by trap-nets and angling in Wakasa Bay, the Japan Sea, from December of 1956 to November of 1957, are analysed qualitatively and quantitatively with a view to clarifying the food elements and their variations with the four seasons. Among the stomach contents have been found 12 different fish species, 1 species of the squid (family Ommastrephidae) and 1 species of Schizopoda (family Mysidae). The food elements of major importance to the fish include horse mackerel (Trachurus japonicus), anchovy (Engraulis japonica), pilchard (Sardinops melanosticta) and common squid (Ommastrephes sloani pacificus), as shown in Figs. 1 and 2. Those of secondary importance consist of cardinal fish (Apogon semilineatus), red porgy (Chrysophrys major), snapper (Parapristipoma trilineatum), silver perch (Leiognathus nuchalis), barracuda (Sphyraena japonica), chub mackerel (Scomber japonicas), puffer (Fugu niphobles), porgy (Argyrops bleekeri), and stargazer (Uranoscopus japonicas). The present study of the stomach contents has shown an increase of the horse mackerel and a decrease of the chub mackerel either in occurence or in amount, being widely different from the results brought about by the previous investigators about twenty years ago, in the point of the former species being less and the latter one more found in the stomach contents. It is a remarkable fact that recently the catch of horse mackerel in Wakasa Bay has been little or no change, or rather a slight increase, while, in the catch of the chub mackerel in the same area, there has been a remarkable decrease, which is presumably the case with the other fishing grounds in the Japan Sea. There may be some probable correspondence between the increase of the horse mackerel in the composition of the yellow-tail's stomach-contents and a good catch of the same species, and also between the decrease of the chub mackerel in the composition of stomach contents and a poor catch of the same species. It is found that there is such correlation between the composition of the stomach contents of the yellow-tail and the seasonal fluctuation in the catch of several fishes (Fig. 2, and Fig. 3, A and B). Judging from these facts, a qualitative and quantitative analysis of the food composition in the stomachs of large fish, such as the yellow-tail, will enable us safely to predict the rela-tive abundance of some useful fish. There is no marked difference in the composition between the stomach contents of the young yellow-tail and those of the adult one.